"Terry" hath wroth:

Does the 2v headway allow for noise spikes. Tants often fail this way.

Tantalums are quite different. Exceed the voltage specification and
they catch fire and burn. It's quite impressive. You can accellerate
the process by reversing the voltage across the tantalum. Try it.
Just take a random small tanatalum and put it across a power supply.
First, it starts to get hot. Then it glows red. Finally, it bursts
into flames and spews toxic smoke. It does take a while to break
down. I've had the polarity reversed for perhaps 3 hours before it
flamed out.

The 2V headway is not for noise spikes. It's to derate the capacitor
voltage specification at high temperatures to extend the lifetime.

Reliability of Capacitors
http://www.illinoiscapacitor.com/uploads/papers_application/85560DAA867C4AE2871F2EFA1749A6C7.pdf

http://www.illinoiscapacitor.com/techcenter/lifecalculators.asp
The upper calculator is for electrolytics.

The primary cause of short lifetime is temperature (and self heating),
but insufficient voltage derating is a close second. Note that at
rated voltage and temperature, the lifetime of an electrolytic is
specified at either 1,000 or 10,000 hrs, depending on service type.
That's not very long. The designed is expected to derate the applied
voltage and operating temperature in order to extend the lifetime. A
2:1 derating will be good for a lifetime of about 15 years. A 2v out
of perhaps 15v derating, might be good enough to barely make it
through the warranty period.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558